The present invention relates generally to electronic display indicators, and more particularly, to an electronic liquid crystal display indicator having a backlighting module therein.
Electronic liquid crystal displays may be used in a variety of applications including, for example, use in aircraft instrument panels as flight indicators, in military tank instrument panels, and in submarine guidance instruments, just to name a few of the many applications for such devices. Previously known display indicators have suffered from various drawbacks. For example, flight indicators have not been very reliable. Periodic failures result in an aircraft being taken out of service until the instrument can be replaced.
Another drawback that display indicators have suffered from is maintaining display visibility in all lighting environments. In military applications the advancement of night vision capability has placed a requirement on electronic guidance indicators to be visible at low levels of backlighting luminance during nighttime operation and night vision equipment usage. Low level luminance prevents the excitation of night vision equipment. Previously known indicators have not had the desired low level, yet visible luminance, required for night vision capability. Another lighting problem of an opposite nature has been bright sunshine penetrating aircraft cockpits making it very difficult to see the display. This occurrence requires high luminance capability from the backlighting source to make the display clearly visible to the pilot. Known backlighting luminance has not achieved desired results.
Maintenance on known guidance system indicators has also been problematic. Ordinarily if one part was in need of repair several other components of the unit would have to be removed in order to replace the broken component. For example, to replace a broken lamp one or more manhours has typically been needed. A need exists to overcome the aforementioned disadvantages.
The present invention comprises an electronic liquid crystal display indicator having a modular lamp design which may be easily removed and replaced. The lamp module provides the capability for high luminance levels never before achieved on such indicators while further providing low level, flicker free luminance for night vision applications. The liquid crystal display (LCD) technology of the present invention is capable of producing a guidance system display on a viewing screen of the indicator unit. The technology may be further enhanced to include an active matrix liquid crystal display (AMLCD) consisting of a series of rows and columns of red, green, and blue dot transistors sandwiched between two glass panels. There may be a plurality of columns of dots going across the display as well as a plurality of vertical rows of dots resulting in a multitude of individual transistor switch dot triplets of red, green and blue. The liquid crystal display is driven by electronics that may be contained within a body or chassis portion of the indicator assembly.
The guidance indicator assembly of the present invention may include a body or chassis, a mounting flange assembly, a lamp module, and a bezel for the face of the indicator. In the present invention, the backlighting may be removed from the chassis to immediately adjacent the front mounting flange in a lamp module housing. This provides more physical space to place a light source and to allow for an increased viewing area for the indicator. Furthermore, locating the backlighting immediately adjacent the display screen reduces stray light losses, while focusing the backlighting directly onto the display area.
In a preferred embodiment of the present invention, one or more hot cathode fluorescent lamps are secured within and form a part of a lamp module. The lamp module is preferably a one-piece self-contained aluminum housing. A wide range of luminance may be provided with the present invention. High levels of luminance are obtained with the use of particular lamps and a unique lamp configuration along with the location of the lamps very near the display screen. Low level luminance is obtained without flickering by driving the fluorescent lamp(s) with an AC wave form using a burst modulation scheme. Burst modulation may be accomplished by providing a voltage to the lamps with the filaments off then providing a voltage to the filaments when the lamps are off. This process eliminates flickering which is caused by cross-modulation.
The present invention will be better understood from the following description of the drawings and detailed description of preferred embodiment(s).